1. Field of Invention
The invention relates to an optical disk system that records an image on an optical disk on which images can be drawn by irradiation of laser light, an optical disk recording apparatus, an image drawing method and an optical disk.
2. Description of Related Art
Optical recording media (optical disks) where information is recorded only once by laser beam irradiation are known. Such optical disks, often called recordable CD's (so-called CD-R), have a typical structure wherein a information recording layer containing an organic dye, a light-reflectance layer of a metal such as gold, and a resin protective layer are formed on a transparent disk-shaped substrate in that order. Information is recorded on a CD-R by irradiation of a laser beam in the near-infrared region onto the CD-R (normally, laser beam at a wavelength of around 780 nm). In the irradiated area of the information recording layer light is absorbed, there is a resulting localized increase in temperature, and this changes its physical and chemical properties (e.g., pit generation). Because of these physical and chemical changes the optical properties are changed and information can be recorded. Reading of the information (reproduction) is also carried out by irradiating with a laser beam having a wavelength the same as that of the recording laser beam. Information is reproduced by detecting the difference in reflectance between areas where the optical properties of the information recording layer have been changed (recorded area) and areas where they are not changed (unrecorded area).
Recently, there is an increasing need for optical recording media higher in recording density. To satisfy this need, an optical disk called a Digital Versatile Disc (so-called DVD-R) has been proposed. The DVD-R has a structure wherein two discs, each consisting of a information recording layer containing a dye, normally a light-reflectance layer over each information recording layer, and also a protective layer as needed, are formed on transparent disk-shaped substrates. On the disk-shaped substrates there are guiding grooves (pregrooves) for tracking an irradiation laser beam, formed of a width of half or less (0.74 to 0.8 μm) of those of a CD-R. These two disks are laminated together, with an adhesive, on the information recording layer side. Alternatively two disks of the above construction can be laminated together with a disc shaped protective layer laminated between them on the information recording layer side. Recording and reproduction of information on and from the DVD-R are carried out by irradiation of a visible laser beam (normally, a laser beam having a wavelength in the range of 630 to 680 nm), and the recording density of a DVD-R can be made higher than that of a CD-R.
There are some known optical disks whereon a label is adhered onto the surface opposite to the recording surface. Such a label carries printed visible image information such as the song title of the audio data recorded on the recording surface, and other titles for identifying the recorded data, and the like. Such optical disks are prepared by printing the titles and the like on a circular label sheet by using, for example, a printer, and then affixing the label on the surface opposite to the recording surface of the optical disk.
However, as described above, preparation of an optical disk carrying a label, on which desired visible images such as title are recorded demands a printer in addition to an optical disk drive. Accordingly, it requires the cumbersome procedure of recording information on the recording surface of an optical disk in an optical disk drive, then removing the optical disk from the optical disk drive, and affixing a label printed by a separate printer.
In view of this, an optical disk recording apparatus capable of drawing an image on the label surface as well as recording and reproducing the information by using laser light has been proposed (as disclosed in Japanese Patent Application Laid-open (JP-A) No. 2003-203348). This optical disk recording apparatus is made for an optical disk having a thermosensitive layer on the label surface, and makes a visible image by scanning a laser pickup and imagewisely irradiating laser light onto the thermosensitive layer (or an image recording layer) to change the color of the irradiated portions.
Further, various kinds of optical disks capable of representing visible information using a contrast caused by difference of reflection between a laser-light-irradiated part and a non-laser-light-irradiated-part on a surface opposite to the information recording layer for recording digital information have been proposed (for example, as disclosed in a JP-A Nos. 2000-113516, 2001-283464, and 2000-173096).
Images with higher quality may be formed by making the image-recording side of the optical disk recognizable by a disk drive by forming pre-pits at the image-recording side of the optical disk having an image-recording layer, or by recording the optimum drawing conditions for each disk on pre-pits, in order to draw images based on the conditions, by reading them when the image is drawn.
In view of saving hardware resources, it is advantageous to use the same laser light as the laser light used for recording and playback of the information recording layer for reading the pre-pits when the pre-pits are formed at the image recording side. Specifically, when the information recording layer is of DVD standard, for example, information is recorded and reproduced with such a laser light having the above-mentioned wavelength (from 630 to 670 nm), and it is preferable that information is read by irradiating the same laser light to the pre-pits at the image-recording layer side.
On the other hand, it is not necessary to make the standard the same for the information-recording layer side and the image-recording side with respect to the density of the pre-pits and the modulation method. For example, the information-recording layer could be of the DVD standard while the pre-pits at the image-recording layer side could be of the CD standard. Since CD and related technologies thereof have preceded DVD, they are almost mature technologies which have been used for a long period of time with abundant technical resources such as know-how. Accordingly, it may even be preferable that the image-recording layer is of the CD standard even when the information-recording layer side is of the DVD standard. In addition, the CD standard is able to prevent maloperation of erroneously reading an image with an optical disk recording apparatus that is not compatible with image recording, when the image-recording layer is of the CD standard.